The research described in this paper attempts to characterize and model porcelain post insulators in a combined experimental and numerical approach. A detailed study of post insulators has been conducted as part of a larger study to seismically qualify 230 kV vertical-break disconnect switches using IEEE 693 procedures. Several types of post insulators from two manufacturers were initially evaluated by subjecting each two element stack to a cantilever load and measuring how each part of the stack contributed to the top deflection. It was found that rotations at the flange-porcelain connections made a significant contribution to the top deflection. When the entire disconnect switch was subjected to severe ground motions on a shake table, some posts developed cracks in the grout at the lower flangeporcelain connections. Evaluation of the response of posts in pre-shake table tests and shake-table tests of a complete switch assembly showed that it is difficult to assess precisely the influence of post response on switch dynamics. However, posts with cracks in the grout could still enable the switch to be qualified to the IEEE 693 high performance level.